1. Field of the Invention
This invention relates to a gas blending system. More particularly it relates to a system for the accurate mixing of a tracer gas with a carrier gas for use in leak detection operations.
2. Description of the Invention
An important industrial service carried out in a variety of applications is a leak detection service for the detecting of leaks in pipelines or other fluid passages or storage systems. Such service typically utilizes a mass spectrometer or other devices to sample the atmosphere surrounding a point in a system suspected of containing a leak. Helium, which is commonly used for such purposes, is used because it is rare in the atmosphere and rapidly dissipates into the atmosphere. As a result, a leak in one area does not contribute to a high leak reading in another area, as can occur when other tracer gases, such as fluorocarbons or sulfur hexafluorides, are employed. However, helium is expensive to use in its pure form so an inert carrier gas, typically nitrogen, is blended with the helium and then injected into the system to be checked. While the proportions in which the helium, as the tracer gas, will be mixed with nitrogen, as the carrier gas, can vary, a typical helium/nitrogen mixture will commonly be in the 1-2% range, although higher or lower proportions of helium can also be employed.
One approach to the blending of helium and nitrogen gases, or any other desired mixture, is to inject the two gases into the system to be checked for leaks based upon their partial pressures and the required proportions of the components in the blend. Another approach would be to purchase a tube trailer with the gases already blended, with the blend then being injected into the system. A third approach would be to manually adjust the flow of the gas streams to form the desired mixture.
The first approach referred to above requires that the system be allowed to sit for some undeterminate time to allow the gas mixture to homogenize. In addition, this approach incurs the risk of having a tracer-rich or a tracer-lean gas in so-called dead lakes in the system, resulting in either a false positive or a false negative leak indication. The second approach is more costly and requires more equipment since the blended gases are transported to a job site in gaseous form. In addition, if severe leaks exist, it is easily possible to run out of the blend before the leak detection service is completed. In the practice of the third approach, constant adjustment by a technician is required, making this type of leak detection service more costly and less reliable than desired in practical commercial operations.
There is a genuine need in the art, in light of such circumstances, for further advancement in the gas mixing field, particularly with respect to the preparation of helium/nitrogen blends for use in leak detection services. Such need relates to low cost, simpler systems than provided by the second approach, with more rapid mixing of the component gases can be achieved by the first approach. In addition, it is desired to have a system that is more accurate than the third approach, and can be left unattended, so as to save technician time and make the overall leak detection service more cost effective and reliable.
It is an object of the invention, therefore, to provide an improved gas blending system.
It is another object of the invention to provide a gas blending system having enhanced cost effectiveness and reliability.
It is a further object of the invention to provide a gas blending system having enhanced accuracy and automatic control so as not to require constant adjustment during gas mixing operations.
With these and other objects in mind, the invention is hereinafter described in detail, the novel features thereof being particularly pointed out in the appended claims.